Techniques for detecting an abnormal current in various types of electronic apparatus have been heretofore proposed. In such techniques, electronic apparatus subject to detection includes a memory which stores thresholds for determination of an overcurrent in various operation modes of the equipment in the form of a table. The electronic apparatus refers to the table to determine whether or not a measured value of a current passing through the equipment exceeds the threshold for determination corresponding to each operation mode. When the determination is made that the measured value exceeds the threshold for determination, the electronic apparatus determines that the equipment is in an overcurrent state. The above-mentioned techniques are disclosed in Japanese Patent Application Laid-Open Nos. 5-30734 (JP1993-30734A) and 5-276646 (JP 1993-276646 A).
Incidentally, upon determination of an overcurrent in the above-mentioned manner, the threshold for determination to be referred to for determination must be set to a value including a margin (or an allowance) to some extent. The margin must be set to the value allowing for so-called variations among individual cases, as well as the minimum allowance required for determination. Here, the “variations among individual cases (or individual difference)” include variations in operating characteristics resulting from temperature variations incident to the use of the equipment, variations in current characteristics among individual pieces of equipment, and variations in detection characteristics among individual current detecting means.
To set the threshold for determination in electronic apparatus, it has hitherto been necessary that the margin be set to the value allowing for many factors as mentioned above. This makes it difficult for conventional electronic apparatus to detect an overcurrent with high accuracy.
In addition, the conventional techniques have been possible to detect only an overcurrent as an abnormal current, and these techniques could not detect an undercurrent.